I don't know about you guys on here with 870's but I always strip the receiver and clean everything in and out. Last night I was doing a friends for the first time so I was really scrubbing inside the receiver and finished up with two bloody finger tips..Slit me on both finger tips running a rag in the rails to get the build up out. So use a heavy rag or go real slow but even then its possible to slice your self real good on those rails.